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设计监控系统

问题​

如何用 Rust 设计一个监控指标收集和暴露系统？

答案​

架构设计​

基于 metrics crate 的实现​

use axum::{Router, routing::get, response::IntoResponse};
use metrics::{counter, gauge, histogram};
use metrics_exporter_prometheus::PrometheusBuilder;

async fn setup_metrics() -> Router {
    // 初始化 Prometheus 指标导出器
    let builder = PrometheusBuilder::new();
    let handle = builder
        .install_recorder()
        .expect("failed to install recorder");

    // 创建路由
    Router::new()
        .route("/metrics", get(move || {
            let handle = handle.clone();
            async move { handle.render() }
        }))
}

// 在业务代码中记录指标
async fn handle_request() {
    // 计数器：请求总数
    counter!("http_requests_total", "method" => "GET", "path" => "/api").increment(1);

    // 直方图：请求延迟
    let start = std::time::Instant::now();
    // ... 业务逻辑 ...
    let duration = start.elapsed();
    histogram!("http_request_duration_seconds").record(duration.as_secs_f64());

    // 仪表盘：当前连接数
    gauge!("active_connections").set(42.0);
}

中间件自动收集 HTTP 指标​

use axum::{middleware, extract::Request, response::Response};
use std::time::Instant;

async fn metrics_middleware(
    req: Request,
    next: middleware::Next,
) -> Response {
    let method = req.method().to_string();
    let path = req.uri().path().to_string();
    let start = Instant::now();

    let response = next.run(req).await;

    let status = response.status().as_u16().to_string();
    let duration = start.elapsed().as_secs_f64();

    counter!("http_requests_total",
        "method" => method.clone(),
        "path" => path.clone(),
        "status" => status
    ).increment(1);

    histogram!("http_request_duration_seconds",
        "method" => method,
        "path" => path
    ).record(duration);

    response
}

四类黄金指标​

指标类型含义
请求速率（Rate）CounterQPS/RPM
错误率（Errors）Counter4xx/5xx 占比
延迟（Duration）HistogramP50/P95/P99
饱和度（Saturation）Gauge连接数、队列长度

常见面试问题​

Q1: Counter vs Gauge vs Histogram？​

答案：

  • Counter：只增不减，例如请求总数、错误总数
  • Gauge：可增可减，例如当前连接数、内存使用量
  • Histogram：采样分布，例如请求延迟的 P50/P95/P99

相关链接​